EMI/RFI SOLUTIONS Electro-Magnetic Compatibility VISHAY INTERTECHNOLOGY, INC. I/O CCFT TFT CONTROLLER LCD RF BASEBAND CONNECTOR RECEIVER P.A. POWER SUPPLY I / O DISPLAY PORT GRAPHIC IC GATE ARRAY CPU VRAM RAM ROM AUDIO PORT LCD I/O BATTERY DC SERIAL PORT AUDIO ANTENNA AUDIO OUT ARRAY DRIVER GYRO GPS VCC VCC VIDEO COMPUTER AUTOMOTIVE TELECOMMUNICATIONS ENGINEERING SOLUTIONS
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EMI /RF I SOLUT IONSE l e c t r o - M a g n e t i c C o m p a t i b i l i t y
V I S H A Y I N T E R T E C H N O L O G Y , I N C .
I/O
CC
FT
TFT CONTROLLER
LCD
RF
BASE
BAN
D
CON
NEC
TOR
REC
EIVE
RP.
A.
POW
ERSU
PPLY
I/O
DIS
PLAY
PO
RT
GR
APH
IC
IC
GAT
E AR
RAY
CPU
VR
AM
RAM
RO
M AUDIO PORT
LCD
I/O
BATTERY
DC
SER
IAL
PORT
AUDIOANTENNA
AUDIOOUT
ARRAY
DRIVER
GYRO
GPS
VCC
VCC
VIDEO
COMPUTER
AUTOMOTIVE
TELECOMMUNICATIONS
EN
GIN
EE
RIN
G S
OL
UT
ION
S
Electro-Magnetic Interference (EMI) and Radio Frequency
Interference (RFI) is noise at radio frequencies generated
by today’s sophisticated electronic equipment’s micro-
processors, oscillators, and switching power supplies. Radio
Frequency (RF) noise is often of sufficient strength as to interfere
with, or even disable, operation of both consumer and vital com-
munication services (i.e., police, fire, emergency medical and mil-
itary). To reduce or eliminate EMI/RFI most countries have insti-
tuted regulations and practices for the design, building and testing
of new electronic equipment so it does not create (or become sus-
ceptible to) EMI/RFI. This area of engineering is often referred to
as Electro-Magnetic Compatibility (EMC). The following infor-
mation is designed to assist the EMC engineers and technicians in
the proper selection of passive components to reduce EMI/RFI.
Components designed for electromagnetic interference filtering
(EMI) or radio frequency interference suppression (RFI) can be
classified into five main categories: L–Reflection (inductors,
common-mode chokes, and transformers), Z–Absorption (ferrite
beads), C–Bypass (ceramic capacitors, film capacitors, varistors),
R–Attenuation (resistors-attenuators), and C+R–Multifunction
(thick film capacitor and resistor combinations and termina-
tions). The choice of component depends on how and where
noise is being generated, and how and where the application cir-
cuit will be operated in the customer’s end product.
REFLECTION
INDUCTORS
The first and most common type of electromagnetic filter is the
inductor or choke. Inductors are used for both line filtering and
energy storage. If a circuit is suspected of generating EMI, a well-
chosen inductor often can help eliminate the problem. For radiated
interference, a toroidal inductor is often called for. Whether in
surface-mount or leaded packaging, a toroidal inductor can virtu-
ally eliminate radiated fields thanks to its unique ability to contain
the magnetic flux within its core. The toroid configuration is also
less susceptible to induced noise from other components since
the applied magnetic field tends to create equal and opposite currents
inside the toroid, thus canceling out the effect of interference.
COMMON-MODE CHOKES
Common-mode or differential-mode chokes are used to eliminate
noise on a pair of conductors. Noise is “common mode” when it
is present or “common” to both conductors. It is usually induced
by the antenna effect of a conductor or printed circuit board (pcb)
trace. Common-mode noise is typically “in phase” in the con-
ductors. Differential noise is present on only one conductor or
present in opposite phase in both conductors. Common-mode
chokes use the properties of two closely coupled magnetic fields
to eliminate the interference problem by canceling the noise within
the magnetic fields. They are best employed to eliminate noise or
EMI on cables or signal tracks.
The choke should be located as close as possible to the driver or
receiver circuit, or at the signal entry point to the circuit board.
Careful selection of an inductance value helps in matching line
impedance and in providing bandwidth filter for the circuit.
Chokes can be configured in the common mode or differential
mode depending on the application.
TRANSFORMERS
A transformer provides an isolation barrier between a signal line
and the signal processing circuit, particularly where the signal
line exits the board or system. Whether the signal is being driven
or received, isolating the line reduces common-mode noise and
eliminates ground potential (or signal return) differences
between systems.
High noise immunity is especially important in thyristor/triac driv-
ing circuits, where the transformer provides an isolation between
the driven load and a logic-based controller. An isolating pulse
transformer provides much better noise immunity than an insulated
gate bipolar transistor (IGBT) due to its inherently lower coupling
capacitance, which is usually measured in tens of picofarads as
opposed to nanofarads for a power IGBT. The lower coupling
capacitance improves the circuit’s immunity from noise generated
by the mains or by power switching devices, and many different
configurations are available to meet the needs of specific designs.
ABSORPTION
SURFACE-MOUNT FERRITE BEADS
Ferrite chip beads, also known as chip impeders, remove RF
energy from pcb traces. In this task, they function as high-fre-
quency resistors that allow DC to pass while absorbing the RF
energy and dissipating that energy in the form of heat. Compared
with alternative solutions, surface-mount ferrite beads are small,
lightweight, and inexpensive. Their high impedance values
L
Z
2
INTRODUCTION TO EMC COMPONENTS
remove a broad range of RF energy while a closed magnetic cir-
cuit design eliminates crosstalk. Because of the bead’s resistance
characteristics at RF frequencies, spurious circuit oscillations or
resonances are reduced.
To select the best bead for the application, the designer needs to
know how much signal attenuation is required, the range of
unwanted frequencies, the source of the electromagnetic energy,
and the environmental and electrical conditions under which the
circuit will operate.
Selection of the right bead for a particular frequency is not always
a simple process, since beads are only rated for impedance at 100
MHz and thus may or may not be optimal for circuits operating at
higher or lower frequencies. DC bias will also lower the effective
impedance of the device. Formerly, the selection process would
have involved the study of several different graphs. Today there
are available automated design tools like Vishay’s Surface Mount
Ferrite Bead Designers Kit (pictured on page 3) to assist designers
in making the correct choice.
BYPASS CAPACITORS/VARISTORS
CERAMIC CAPACITORS
Ceramic capacitors are often used to reduce EMI by shunting the
unwanted signals to ground. Ceramic capacitors are available in
many different configurations and sizes; choosing the right capacitor
for the application depends on the electrical characteristics of the
noise and the associated electrical circuit. Peak circuit voltage, fre-
quency spectrum of both the wanted and unwanted signals, and
energy content of the unwanted signal all play an important part in
selecting the correct ceramic capacitor for EMI filtering. It is
important when using capacitors as EMI filters to insure that the
circuit has a stable ground. The impedance of circuits using
ceramic capacitors as EMI filters are characterized by high impedance.
TYPE X AND Y RFI CAPACITORS
RFI Capacitors are used to reduce interference that is conducted on
the AC line either in common mode or in differential mode.
Differential-mode interference can be envisioned as a noise source
connected between the main and neutral wires. A properly applied
type X (or “line-to-line”) capacitor is an effective solution for this
case. Common-mode interference is represented by a source between
either main or neutral and chassis ground, and the appropriate solu-
tion is a type Y (or “line-to-ground”) capacitor to provide filtering.
X capacitor values are determined by the frequency spectrum of
the offending noise sources and therefore can be any available
value, although they typically range from 0.1µF to 1.0µF, and are
metallized film construction. Improved pcb layout practices can
allow these values to be reduced. Two smaller value X capacitors
are usually a better solution than one larger value X capacitor,
especially when used in a pie filter configuration with a choke. Y
capacitors are normally ceramic and have values that are restricted
typically to values around 4700pF to reduce to a minimum
50/60Hz leakage current to ground. The diagram (below left) of a
noise suppression solution on an AC Power line shows the nor-
mal use of both X and Y type capacitors.
X Capacitor Applications. X Capacitors are suitable only for
applications where there is no danger of a short-circuit resulting
in an electric shock. X type capacitors are divided into subclasses
corresponding to the peak voltages to which they are subjected in
addition to the power line voltage. All three classes are described
Common mode choke coil suppresses common mode noise
Line bypass capacitor (Y-capacitor)suppresses common mode noise
C
Subclass Peak pulse voltage√p in operation
Application
Use for high peakvoltages
General purpose
For C ≤ 1,0 µF: Vp = 4,0kV
For C > 1,0 µF: Vp = 4,0 kV1)√CN
For C ≤ 1,0 µF: Vp = 2,5kV
For C > 1,0 µF: Vp = 2,5 kV1)√CN
2,5 kV <Vp ≤ 4,0 kV
Vp ≤ 2,5 kV
Peak values of surge voltageVp (before endurance test)
X1
X2
MAIN X TYPE CAPACITORS
Subclass Type of bridgedinsulation
Rated AC voltage
VR ≤ 250V
150V ≤ VR ≤ 250V
8,0kV
5,0kV
Double or reinforced
Basic or supplementary
Peak values of surge voltageVp (before endurance test)
Y1
Y2
MAIN Y TYPE CAPACITORS
ELECTRO-MAGNETIC COMPATIBILITY
3
4
Y Capacitor Applications. Capacitors connected between power
lines and ground (Y capacitors) have the potential upon a loss of
earth ground to pass current from the device ground (metal case)
by means of capacitive leakage current. Y capacitors are designed
to limit the leakage current so that no dangerous voltages or cur-
rents can occur on exposed metal parts resulting in personal
injury or death. This leakage current is even more restricted in
medical type equipment. In ordinary data processing equipment,
class Y2 is generally required when bridging the AC primary to
ground. Some applications such as bridging the DC side of the
primary to ground may require a Y1 type.
RFI CAPACITOR CONSTRUCTION
There are two types of RFI capacitors commonly in use on the AC
line. These are metallized film and ceramic. The ceramic capacitor
was described above. The metallized film are categorized as “self
healing” while ceramic is not. The property of self healing, prop-
erly designed into a capacitor, can extend its life while maintain-
ing a small size and safe operation.
VARISTORS
A varistor is used to protect sensitive circuits from excessive voltage
excursions or spikes that could damage components. The diagram to
the right shows typical characteristics of voltage transients by peak
voltage and transient duration in microseconds. A varistor acts as a
short to voltage excursions or spikes that exceed the specified voltage
of the varistor. By allowing voltage transients to be bypassed to ground
a varistor can prevent circuit damage and reduce EMI problems.
ATTENUATION
A resistor is used to attenuate signals or to maintain signal integrity
while reducing power consumption through the conversion of the sig-
nal’s electrical energy into heat. Excess noise is often generated in cir-
cuits because of impedance mismatches between circuits that result in
overdriving of components that can lead to the production of unwant-
ed harmonics (noise). Matching circuit impedance and attenuating sig-
nals between circuits is often done using a complex network of inde-
pendent resistors. This same goal can be accomplished using a signal
chip that is designed to duplicate the resistor network on a single chip.
Every resistor is performing similar because of the usage of the same
substrate and batch. This type of device is referred to as a chip attenu-
ator and can help prevent EMI.
MULTIFUNCTION
A resistor and capacitor combination is often the simplest, most com-
pact and inexpensive way to provide the filtering function. With thick
film or thin film technology, a resistor/capacitor filter can be built for
either a low-pass or high-pass response depending on the schematic
chosen. Values can be adjusted to filter a wide range of frequencies
found in RF designs. These R/C filters can take the form of a single
chip, or an array can be used where multiple signal lines need a partic-
ular frequency response. R/C filters are used for lines with no resistive
termination. Thin film resistor/capacitor networks provide substantial
space savings with exceptional performance.
EMI/EMC COMPONENT SELECTION
Once the designer knows which circuit paths and circuit areas are
likely to conduct noise—and which circuit areas are likely to act as
antennas and radiate noise—the most appropriate location for the
components chosen can be determined. The choice of components will
depend on the frequency and signal level of the noise to be eliminated.
Naturally consideration must also be given to the frequencies that
should be left intact.
Another consideration is the circuit impedance. The diagram to the
right shows the relationship between impedance and the type of
filter to be used.
C R+
1.2kV
6kV
800V
400V
Transient Peak (kV)
10–
1–
TYPES OF TRANSIENTS FOUND ON THE LINE
–A
B
C
D
A = 0.1µS/6kV Atmospheric interference such as lightning.B = 60µS/1.2kV Failure in the network or in nearby equipment,
such as flashovers and fuse breakings.C = 200µS/800V On/off operation of equipment such as motors,
air conditioning units, etc.D = 1000µS/400V Pulses from equipment such as welders, thyristors, triacs, etc.
R
Weak spot
Dielectric Metallization
0.1 10.1 10 100 1000µS
Weak spot removed
Heated material
THE PROCESS OF SELF HEALING
In high-speed signal circuits, the easiest choice is a pure resistor
termination followed by R/C filter terminations. The best choice is a
complex filter consisting of inductive and capacitive components.
In lower-speed circuits, grounding stability must be determined
first. Capacitive EMI components are an excellent choice when a
stable ground is available, but if the circuit has an unstable
ground, designers should consider using inductive components
that can provide sufficient impedance to the noise to reduce it
below the acceptable threshold for EMI or RFI.
Oftentimes it will be possible to measure the overall radiation
level from a given piece of equipment only at the end of the design
process, so choosing the wrong component can have adverse
consequences downstream. Although some measure of trial and
error may always be necessary, designers can minimize wasted
time by observing the following rules:
• Always place EMI/EMC components as close as possible to the
noise source.
• Select EMI/EMC components that match the impedance of the
noise conduction path, whether or not this is the same as the
circuit path. Remember that common-mode noise tends to
travel in a different path from circuit current.
• Always begin the design process with EMI/EMC components
that offer more than sufficient performance to meet emission
standards. There is always time to work on reducing component
costs once a working design is developed.
RELATIONSHIP OF IMPEDANCE TO TYPE OF FILTERS USED
Line Impedance
Effective Impedance Calculator
ILB-1206Surface
Mount Bead
Above is a representation of the calculator included in Vishay’s SurfaceMount Ferrite Bead Designers Kit. The kit is available upon request.
FREQUENCY
DC BIAS CURRENT
EXAMPLE:Determine the ZE for a 150 & 600Ohm bead at 900MHz, and with aDC bias current of 300mA.STEP 1:Move pointer to 900 MHz Position.STEP 2:Read the Ze in Window Under 150Ohm Bead (146 Ohms) & 600 OhmBead (89 Ohms).STEP 3:Move pointer to 300 mA Position.STEP 4:Multiply the Values From Step 2 bythe % Listed Under the 150 Ohmand 600 Ohm Beads in the % of Ze Window todetermine Ze with DC Bias.FOR EXAMPLE:Ze ñ 146 Ohms x 53.6% = 78.2(ILB-1206 150 Ohm)Ze ñ 89 Ohms x 50.5% = 45.0(ILB-1206 600 Ohm)
DDNL0409–2 4.3 x 9mmDDM20312–2 3 x 12mmDDML04... 4.3 x 9–20mm
1600 / 400V5000pF / 200V1600– 7000pF/ 400V
Type – Class (DxL) Capacitance / VDC
FEED THROUGH FILTERS
F1740–15 – X1
F1740–35 – X1Y2
F1740–55 – X1Y2
.0068 – .47uF / 275V
.022 – .47µH / 275V+2X (2700pF –.027uF) / 275V
.022 – .47 / 275V+2X (2400pF –.027uF) / 275V
Type – Class Capacitance / VDC
RFI CAP PAPER
W1X – X1 4700pF–.22uF / 275V
Type – Class Capacitance / VDC
RFI CAP CERAMIC
WYO
VKO
WKO
VKP
WKP
1000pF – .22uF / 250 (Y2)
1000 – 4700pF / 440 (X1)/ 250 (X2)
33 – 4700pF / 440 (X1)/ 250 (Y2)
470 – 4700pF / 760 (X1)/ 500 (Y1)
33 – 4700pF / 440 (X1)/ 250 (Y1)
Type Capacitance / VDC (Class)
RFI CAP CERAMIC – SAFETY DISC
BYPASSNoise elements in the signals are shunted to ground and preventedfrom entering the load. Very effective for high impedance lines.
F1772
F1740
RX
WYO-102
WKO-101
WKP-472
VP31
VP31
13
EMC LEADED DEVICESPOWER LINE AND SIGNAL LINE USE
MKP1842
ELECTRO-MAGNETIC COMPATIBILITY
C
Note: Case sizes are listed in EIA standard sizes. Unless stated otherwise, case sizes use inches: e.g., 0805 equals .08 in long by .05 in wide.
14
GLOSSARY OF TERMS
For ELF/VLF: ZO = √ R/G ohmsFor frequencies > 10 kHz: ZO = √L/C ohms
AF Audio Frequency. Components of signal or noise having fre-quencies in the 15Hz–20kHz range.
ANSI American National Standards Institute
ANSI/IEEE C95.1-1992 Recommendation for limits of maximumhuman exposure to radiated fields.
Case Size The physical size of a component. Vishay sizes are usual-ly included in the part number. “0805” means the device is .08″ longand .05″ wide. The case size is usually followed by the parts value.
Capacitor A passive component whose reactance, Xc= 1⁄2π f, decreas-es with frequency at 20 dB/decade.
Capacitors, Feed Through Single-stage capacitors that are bulkheadmounted to provide low insertion inductance.
CCIR International Radio Consultative Committee
CE Mark European product compliance (conformity) mark
Certification (FCC) A procedure that requires submittal of a writtenapplication to the FCC that includes an application form 731, fee,complete technical description of the product and a measurementreport showing compliance with the FCC technical standards.
Characteristic Impedance The equivalent circuit of a transmissionline, Zo, defining if lossy and reactive properties:
Chip Bead A generic term for a ferrite component (“bead”) that isproduced in a surface mount package. A chip bead already has aninternal conductor inside, so no additional parts are necessary tomake the component work.
Common Mode When applied to two or more wires, all currentsflowing therein which are in phase.
DC Current Rating The maximum amount of direct current that cansafely pass through the component.
DC/DC Converters These devices are used in DC power-distribu-tion, and convert DC voltage from one level to another DC level.
Differential Mode On a wire pair when the currents are of oppositepolarity.
EMC Electro-Magnetic Compatibility. The practice of building elec-tronic devices so that they do not create (or are susceptible to)EMI/RFI.
EMI When an electrical disturbance from natural phenomena or anelectrical/electronics device or system causes an undesired responsein another.
ESD An electrostatic discharge with a fast risetime, intensivedischarges from humans, clothing, furniture and other chargeddielectric sources.
FCC Federal Communications Commission. Mission: to manage thespectrum and provide leadership in order to create new opportunitiesfor competitive technologies and services for the American public.Website: http://www.fcc.gov.com
Ferrites Powdered magnetic (permeable) material in the form ofbeads, rods and blocks used to absorb EMI on wires and cables.Ferrites convert the associated EMI magnetic-flux density into heat.
Ferrite Beads A ferrite core with a conductor passing through theferrite (as opposed to wrapping the wire aroune the ferrite). Thesedevices resemble a bead in a necklace. Ferrite beads are also availablein a surface mount package.
Harmonic An integer multiple of the fundamental frequency.
HF High frequency: frequency ranging from 3 MHz to 30 MHz.
IEC International Electrotechnical Commission
IEEE Institute of Electrical and Electronic Engineers
IEEE/EMC The EMC Society (professional group) within the IEEE.
Impedance The vector sum of resistance and reactance at any spec-ified frequency, where the reactance corresponds to that of an induc-tor or capacitor, as applicable.
Inductor A passive component whose reactance, XL= 1⁄2π f, increaseswith frequency at 20 dB/decade.
Inductors and Coils Discrete devices used to pass low-frequencyand reject high-frequency EMI. Often used in filters, safety-groundlines with ferrites and oscillator tank circuits.
I/O input/output (port or cable)
LF Low frequency: frequency ranging from 30 kHz to 300 kHz. Thisincludes many navigation bands, including Loran.
Maximum DC Resistance The maximum value of resistance (howmuch opposition there is to current flow) that will be exhibited bythe device.
MOV Metal-Oxide Varistor
Radio Frequency In the ANS/IEEE, Standard 1001984, the term iscommonly used to cover the frequency range from 10 kHz to 1000 GHz.
RFI Radio Frequency Interference. Exists when either the transmit-ter or receiver has an antenna, causing undesired interference withother equipment or systems.
SMD Surface Mount Device. An electronic component without wire-type external leads; the solder terminals are built as an integral partof the component.
Surge A sudden voltage increase on the power mains.
Transformer A device for changing the voltage of electrical energy.
15
ELECTRO-MAGNETIC COMPATIBILITY
EMI REGULATIONS
NOISE DETECTION
EQUIPMENT
Generic Standard
ITE (Information technology*)
ISM (microwaves)
Igniters (autos, motorboats)
Radio, TV,audio, VTR
Household electrical,portable tools
Fluorescent lamps,luminary
Transceiver
Power supply higher harmonte
Basic Standard
Generic Standard
Industry processmeasurement & control
Radio, TV
ITE (Information technology)
INFORMATION
IEC61000-6-3 IEC61000-6-4
CISPR Pub. 22
CISPR Pub. 11
CISPR Pub. 12
CISPR Pub. 13
CISPR Pub. 14
CISPR Pub. 15
CCIR
IEC555IEC61000-3
IEC61000-4
IEC61000-6-1 IEC61000-6-2
IEC801 series
CISPR Pub. 20
CISPR Pub. 24
JAPAN
VCCI Electrical ApplianceRegulation
Electrical Appliance Regulation
JASO
Electrical Appliance Regulation
Electrical Appliance Regulation
Electrical Appliance Regulation
Radio Act
Industry Voluntary Regulation
(JIS regulation pending)
(JIS regulation pending)
Industry Voluntary Action
Industry Voluntary Action
Industry Voluntary Action
UNITED STATES
FCC Part 15 Subpart B
ECC Part 18
FCC Part 15 Subpart B
FCC Part 15 Subpart B
FCC Part 15 Subpart CFCC Part 22
EUROPE
EN50081-1EN50081-2
EN55022
EN55011
Automotive Directive
EN55013
EN55014
EN55015
ETS300 Series
EN60555EN61000-3
EN61000-4 Series
EN50082-1EN50082-2
EN55020
EN55024
EM
ISS
ION
IMM
UN
ITY
ITEM MEASURED:
POLARIZATION &MEASURING POINT:
FREQUENCY (Hz):
DETECTION:
MEASURING DEVICE:
Radiated interference
Horizontal Pol./ Vertical Pol.
30M to 1GHz
Quasi-Peak
Antenna
CISPR PUB 22
*printers, personal computers, word processors, displays
Radiatedinterference
Horizontal Pol./ Vertical Pol.
30M to 1GHz
Quasi-Peak,Mean
Antenna
Mains interferencevoltage
AC Mains Ports
450k to 30MHz
Quasi-Peak
Artificial MainsNetwork
Radiated interference
Horizontal Pol./ Vertical Pol.
30M to 1GHz
Quasi-Peak
Dipole antenna
Mains interferencevoltage
AC Mains Ports
150k to 30MHz*
Quasi-Peak,Mean
Artificial MainsNetwork
Mains interferencevoltage
AC Mains Ports
150k to 30MHz
Quasi-Peak,Mean
Artificial MainsNetwork
VCCI FCC PART 15 EN55022
*for 150kHz to 526.5kHz, design targets only at this time
Specifications are subject to change without notice.
All details in printed form are legally binding especially with respect to the provisions of §§463 and 480 II of the German Code of Civil Law afterwritten confirmation only. The data indicated herein described the type of component and shall not be considered as assured characteristics.
The products listed in this catalog are not generally recommended for use in life support systems where a failure or malfunction of the compo-nent may directly threaten life or cause injury.
The user of products in such applications assumes all risks of such use and will agree to hold Vishay Intertechnology, Inc. and all the companieswhose products are represented in this catalog, harmless against all damages.